This invention generally relates to a method and apparatus for automatically protecting personnel from direct exposure to the output of a high intensity light source. More specifically, this invention relates to a method and apparatus for protecting the eyes from direct exposure to high intensity light used in medical devices such as endoscopes and the like. Additionally, the risk of inadvertent ignition of combustible material, such as paper surgical drapes, caused by close proximity to high intensity light source outputs, is avoided.
The imaging of body surfaces through an endoscope is well known within the medical and veterinarian fields. Typically, this involves inserting an endoscope into a body cavity and directing an intense light source output through the endoscope to illuminate body tissue. Light reflected by the body tissue then is guided along an optical path to an image sensor to generate a video image of the tissue. One such approach is described in U.S. Pat. No. 5,162,913 to Chatenever, et al, and provides a technique for an automatic adjustment of the exposure of video images detected with a CCD (charge coupled device) image sensor.
The use of high intensity light sources involves potential hazards to medical personnel and patients. For example, when a light guide cable, used to convey the intense light source output, is momentarily disconnected from the endoscope and placed on a sterile drape used to protect the patient, the light output intensity can be sufficient to ignite the drape and pose a fire hazard; or, the user can inadvertently hold the disconnected light guide cable in such a way as to temporarily blind another person in the room. In some instances, when the endoscope is pulled out of a patient, there can be a risk of these same hazards. When the light source is used with an endoscopic video camera, which has an automatic exposure system, the light source may be turned up to an intensity level higher than required for the camera to produce well-exposed images. This increased light intensity level can desiccate body tissue and cause serious injury to the patient. Typically, endoscopic video camera automatic exposure systems can produce well-exposed images with an electronic shutter setting of approximately {fraction (1/125)}th to {fraction (1/500)}th of a second. If an endoscope distal end is placed within close proximity to tissue being imaged, typically, a relatively low light intensity level will still enable an endoscopic video camera to produce well-exposed images. An undesirable, and potentially dangerous, scenario can occur if the light source output is set to a high level, and the endoscope distal end is placed within close proximity to tissue being imaged. Typically, in such a case, camera automatic exposure systems will adjust electronic shutter settings to approximately {fraction (1/10,000)}th of a second (or faster) to compensate for the high illumination reflections from the tissue. In such a situation, the risk of desiccating delicate tissue is greatly increased.
A technique for automatically controlling the light intensity from a light source, on the basis of an image signal from an imaging unit associated with an endoscope, is described in Japanese Unexamined Patent Publication No. 62-155689 as mentioned at column 2, lines 1-21 in U.S. Pat. No. 5,957,834 to A. Mochida. As recognized in the Mochida patent, when light intensity control is made dependent upon a signal derived from the image, then upon removal of the endoscope from the body, the control is likely to increase the intensity level from the light source, when instead it should decrease it to protect the operator""s eyes from accidental exposure and prevent ignition of combustible material. In the Mochida patent a switch is added to manually adjust and control the output of the light source when the endoscope is removed from a body.
As further described in the Mochida patent the intensity level of the light source is controlled by regulating the position of a diaphragm with respect to the light source. The control signal for doing this is derived from an image sensor in the endoscope.
In U.S. Pat. No. 4,527,552 a photoelectric element generates a signal indicative of the intensity of light reflected from an object illuminated by a light source associated with the endoscope to control the light source output level. In U.S. Pat. No. 5,131,381 a light source associated with an endoscope is controlled by a signal that represents the density value of each line of a camera video image derived through the endoscope. Other patents relevant to light intensity level controls for endoscopes are U.S. Pat. Nos. 5,159,380; 3,670,722; 5,134,469; 4,963,960; and 4,561,429.
Techniques have been proposed to reduce the risks associated with high intensity light sources. One involves a special light guide cable with wires in it that are shorted together when the cable is attached to an endoscope. The short is detected at the light source and light intensity is reduced when the cable is disconnected and the short is subsequently removed. A retractable mechanical shroud, which covers the light guide when not connected to an endoscope, has also been suggested.
These safety solutions are not necessarily effective against all potential hazardous conditions that may arise; such as when the endoscope with the light guide cable still attached is pulled out of a patient and inadvertently directed at a person or surgical drape, or when the light guide or source initially is directed to treat openly accessible tissue and inadvertently misdirected during or after a procedure, or when a video camera head, attached to the endoscope light guide cable combination, is disconnected from its corresponding control unit.
With a method and apparatus, in accordance with the invention, the output from a high intensity light source is controlled so that whenever the output is not directed at tissue (meaning that the endoscope/video camera/light source combination is not currently being used to image body tissue), the light source output intensity is automatically reduced to a safe level. This is achieved by monitoring the reflected light from tissue and when this reflection indicates that the light source is not directed at tissue, the light intensity is turned down to a safe level.
As described herein for one preferred form of the invention, the light source is provided with a characteristic signal. The absence of this characteristic signal from reflected light becomes indicative that the light source is not directed at tissue and the light intensity needs to be reduced to avoid inadvertent light related injury. This characteristic signal can be a frequency or wavelength modulation, but preferably is an amplitude or intensity modulation at a distinctive frequency so that the modulation can be detected in reflected light.
In one embodiment, in accordance with the invention, a modulation signal is generated and is superimposed on the high intensity light source output. The light source output thus includes a modulation signal that is also present in reflected light, which can be detected by a video camera imager. The lack of detection of the modulation signal can then be used to indicate when the light source output is not directed at tissue, thus initiating a dramatic reduction in light intensity.
The technique of this invention can be particularly effective in assuring protective control over a high intensity light source used as part of an endoscopic video system utilizing a communication bus to interconnect various devices. In such case, the light source modulation is extracted from the pixel signals at the output of an endoscopic image sensor used to detect light reflected from tissue observed through an endoscope. As long as this modulation signal is detected, the high intensity light source output remains at a level adequate to produce well-exposed video images. However, once the modulation signal either disappears or drops below a specific reference level, it is assumed that the light guide cable is no longer attached to the endoscope, or that the endoscope itself is removed from the patient, and a protective reaction is initiated. The loss or reduction of the modulation signal is thus converted to a control signal that is sent by means of the bus to the light source, causing the output intensity to be turned down to a safe level.
Additionally, as described herein, a method is provided, by the invention, to determine when the light source output exceeds a level necessary for an endoscopic video camera to produce well-exposed images.
It is, therefore, an object of the invention to provide a method and apparatus with which automatic protection of personnel against accidental exposure to high intensity light from a light guide cable, used with or without an endoscope attached, is obtained.
It is a further object of the invention to provide a video camera/light source control for an enhanced safety of the use of an endoscope using the high intensity light source for the illumination of tissue.
It is still further an object of the invention to provide a control over the overall light output from a high intensity light source used to illuminate an object observed through an endoscope.
These and other objects of the invention can be understood from the following detailed description of a preferred embodiment of the invention in conjunction with the drawings.